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A comparative overview of the Animal Kingdom

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A comparative overview of the Animal Kingdom * * * * * * * * * * * * * * * * * * * * * * * * * * * * * General Features of Animals Animals are the consumers of the ... – PowerPoint PPT presentation

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Title: A comparative overview of the Animal Kingdom


1
A comparative overview of the Animal Kingdom
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General Features of Animals
  • Animals are the consumers of the Earth
  • They are a very diverse group
  • -However, they share major characteristics
  • -Are heterotrophs
  • -Are multicellular
  • -Have cells without cell walls
  • -Most are able to move

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General Features of Animals
  • -Are very diverse in form and habitat
  • -Most reproduce sexually
  • -Have a characteristic pattern of
    embryonic development
  • -Cells of all animals (except sponges) are
    organized into tissues

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Evolution of the Animal Body Plan
  • Five key transitions can be noted in animal
    evolution
  • 1. Tissues
  • 2. Symmetry
  • 3. Body cavity
  • 4. Development
  • 5. Segmentation

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Evolution of the Animal Body Plan
  • 1. Evolution of tissues
  • -Parazoa (Sponges - the simplest animals) lack
    defined tissues and organs
  • -Have the ability to disaggregate and
    aggregate their cells
  • -Eumetazoa (all other animals) have distinct and
    well-defined tissues
  • -Have irreversible differentiation for most
    cell types

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Evolution of the Animal Body Plan
  • 2. Evolution of symmetry
  • -Sponges also lack any definite symmetry
  • -Eumetazoa have a symmetry defined along an
    imaginary axis drawn through the animals body
  • -There are two main types of symmetry

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Evolution of the Animal Body Plan
  • -Radial symmetry
  • -Body parts arranged around central axis
  • -Can be bisected into two equal halves in any
    2-D plane
  • -Bilateral symmetry
  • -Body has right and left halves that are
    mirror images
  • -Only the sagittal plane bisects the animal
    into two equal halves

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Evolution of the Animal Body Plan
  • Bilaterally symmetrical animals have two main
    advantages over radially symmetrical ones
  • 1. Cephalization
  • -Evolution of a definite brain area
  • 2. Greater mobility

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Evolution of the Animal Body Plan
  • 3. Evolution of a body cavity
  • -Eumetazoa produce three germ layers
  • -Outer ectoderm (body coverings and nervous
    system)
  • -Middle mesoderm (skeleton and muscles)
  • -Inner endoderm (digestive organs and
    intestines)
  • Body cavity Space surrounded by mesoderm tissue
    that is formed during development

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Evolution of the Animal Body Plan
  • 3. Evolution of a body cavity
  • -Three basic kinds of body plans
  • -Acoelomates No body cavity
  • -Pseudocoelomates Body cavity between mesoderm
    and endoderm
  • -Called the pseudocoel
  • -Coelomates Body cavity entirely within the
    mesoderm
  • -Called the coelom

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Evolution of the Animal Body Plan
  • -The body cavity made possible the development
    of advanced organs systems
  • -Coelomates developed a circulatory system to
    flow nutrients and remove wastes
  • -Open circulatory system blood passes from
    vessels into sinuses, mixes with body fluids and
    reenters the vessels
  • -Closed circulatory system blood moves
    continuously through vessels that are separated
    from body fluids

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Evolution of the Animal Body Plan
  • 4. Evolution of different patterns of development
  • -The basic Bilaterian pattern of development
  • -Mitotic cell divisions of the egg form a
    hollow ball of cells, called the blastula
  • -Blastula indents to form a two-layer- thick
    ball with
  • -Blastopore Opening to outside
  • -Archenteron Primitive body cavity

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Evolution of the Animal Body Plan
  • Bilaterians can be divided into two groups
  • -Protostomes develop the mouth first from or
    near the blastopore
  • -Anus (if present) develops either from
    blastopore or another region of embryo
  • -Deuterostomes develop the anus first from the
    blastopore
  • -Mouth develops later from another region of
    the embryo

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Evolution of the Animal Body Plan
  • Deuterostomes differ from protostomes in three
    other fundamental embryological features
  • -1. Cleaveage pattern of embryonic cells
  • -Protostomes Spiral cleavage
  • -Deuterostomes Radial cleavage
  • -2. Developmental fate of cells
  • -Protostomes Determinate development
  • -Deuterostomes Indeterminate development

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Evolution of the Animal Body Plan
  • -3. Origination of coelom
  • -Protostomes Forms simply and directly from
    the mesoderm
  • -Deuterostomes Forms indirectly from the
    archenteron
  • Deuterostomes evolved from protostomes more than
    500 MYA

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Evolution of the Animal Body Plan
  • 5. Evolution of segmentation
  • -Segmentation provides two advantages
  • -1. Allows redundant organ systems in adults
    such as occurs in the annelids
  • -2. Allows for more efficient and flexible
    movement because each segment can move
    independently
  • Segmentation appeared several times in the
    evolution of animals

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Traditional Classification of Animals
  • Multicellular animals, or metazoans, are
    traditionally divided into 36 or so distinct
    phyla based on shared anatomy and embryology
  • Metazoans are divided into two main branches
  • -Parazoa Lack symmetry and tissues
  • -Eumetazoa Have symmetry and tissues
  • -Diploblastic Have two germ layers
  • -Triploblastic Have three germ layers

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A New Look At Metazoans
  • The traditional animal phylogeny is being
    reevaluated using molecular data
  • Myzostomids are marine animals that are parasites
    of echinoderms
  • -Have no body cavity and only incomplete
    segmentation
  • -And so have been allied with annelids

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A New Look At Metazoans
  • Recent analysis of the translation machinery
    revealed that myzostomids have no close link to
    the annelids at all

-Instead, they are more closely allied with the
flatworms (planaria and tapeworms)
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A New Look At Metazoans
  • Therefore, key morphological characters used in
    traditional classification are not necessarily
    conservative
  • Molecular systematics uses unique sequences
    within certain genes to identify clusters of
    related groups

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A New Look At Metazoans
  • Most new phylogenies agree on two revolutionary
    features
  • 1. Separation of annelids and arthropods into
    different clades
  • 2. Division of the protostome group into
    Ecdysozoa and Spiralia
  • -The latter is then broken down into
    Lophotrochozoa and Platyzoa

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A New Look At Metazoans
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Evolutionary Developmental Biology
  • Most taxonomists agree that the animal kingdom is
    monophyletic
  • Three prominent hypotheses have been proposed for
    the origin of metazoans from single-celled
    protists

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Evolutionary Developmental Biology
  • 1. The multinucleate hypothesis
  • 2. The colonial flagellate hypothesis
  • 3. The polyphyletic origin hypothesis
  • Molecular systematics using rRNA sequences
    settles this argument in favor of the colonial
    flagellate hypothesis

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Evolutionary Developmental Biology
  • Molecular analysis may also explain the Cambrian
    explosion
  • -The enormous expansion of animal diversity in
    the Cambrian period (543 to 525 MYA)
  • -The homeobox (Hox) developmental gene complex
    evolved
  • -Provided a tool that can produce rapid
    changes in body plan

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